2 days ago my breast was red under my nipple & sore. i used a anti-biotic cream & the soreness stopped & looks a light pink/purple. now i feel a lump?

Mastitis: You probably have a partially treated infection there - certainly when it was red and inflamed I would consider that a mastitis. Then, with the use of a localized antibiotic -you killed off some of the bacteria (probably Staph). You're body did some of the work too and now you're left with a partially treated infection. Best to show it to a doc who can help you-if for example drainage is needed.